1. Field of the Invention
The present invention relates to a fusing roller apparatus for an electrophotographic image forming apparatus, and more particularly, to a fusing roller apparatus for an electrophotographic image forming apparatus, which can be instantaneously heated with low power consumption.
2. Description of the Related Art
In a general electrophotographic image forming apparatus such as a copy machine and laser beam printer, as an electrostatic charging roller adjacent to a photoreceptor drum rotates, a photosensitive material coated on the surface of the photoreceptor drum is uniformly charged. The charged photosensitive material is exposed to a laser beam scanned from a laser scanning unit (LSU) so that a latent electrostatic image is formed in a predetermined pattern on the photosensitive material. A developer unit supplies toner to the photosensitive material to develop the latent electrostatic image formed on the photosensitive material into a visible toner image. A predetermined transfer voltage is applied to a transfer roller which is put in contact with the photoreceptor drum at a predetermined force while the photoreceptor drum carries the toner image. In this state, as a print paper is fed in the gap between the transfer roller and the photoreceptor drum, the toner image formed on the photosensitive material is transferred to the print paper. A fixing unit which includes a fusing roller, instantaneously heats the print paper to which the toner image is transferred to fuse and fix the toner image to the print paper. In general, a halogen lamp is used as a heat source for the fixing unit. The halogen lamp is installed inside the fusing roller and heats the surface of the fusing roller to a target temperature with radiant heat.
In a conventional fusing roller apparatus of an electrophotographic image forming apparatus, which uses a halogen lamp as a heat source, the exterior surface of the fusing roller must generate heat; the fusing roller is therefore heated from the inside out by radiant heat from the halogen lamp. A pressure roller is located below the fusing roller. As print paper carrying a toner image in a powder form passes between the fusing roller and the pressure roller, the print paper is hot pressed by a predetermined force and the toner image is fused and fixed to the print paper by the heat and force from the fusing roller and the pressure roller.
A thermistor may be used for detecting and converting the surface temperature of the fusing roller into an electric signal and a thermostat may be used to cut off the power supply to the halogen lamp.
A conventional fusing roller apparatus which employs a halogen lamp as a heat source unnecessarily consumes a large amount of power, and needs a considerably long warm-up period when the image forming apparatus is turned on for image formation. In other words, after the application of power, a standby period follows until the temperature of the fusing roller reaches a target temperature, for example, for a few tens of seconds to a few minutes. We have found that with a conventional fusing roller apparatus, because the fusing roller is heated by radiant heat from the heat source, the rate of heat transfer is low. In particular, compensation for temperature variations due to a drop in the temperature of the fusing roller caused by contact with a print paper is delayed, so that it is difficult to uniformly control the distribution of temperature along the axial length of the fusing roller. Even in a stand-by mode where the operation of the printer is suspended, power must be periodically applied so as to keep the temperature of the fusing roller constant, thereby causing unnecessary power consumption. Also, it takes a considerable amount of time to switch the fusing roller from its stand-by mode to an operating mode for image output, so that the resultant image cannot be rapidly printed.
An alternative design for a conventional fusing roller apparatus employs a heating plate placed in a lower portion of a flexible cylindrical film tube, with a pressure roller mounted underneath the heating plate. The film tube is rotated by a separate rotation unit and is locally heated and deformed at a part between the heating plate and the pressure roller. While this method of locally heating the film tube with a heating plate was thought to be advantageous in terms of low power consumption, it is unsuitable for high-speed printing.
Japanese Patent Application Nos. sho 58-163836 (Sep. 16, 1983); hei 3-107438 (May 13, 1991), hei 3-136478 (Jun. 7, 1991); hei 5-135656 (Jun. 7, 1993); hei 6-296633 (Nov. 30, 1994); hei 6-316435 (Dec. 20, 1994); hei 7-65878 (Mar. 24, 1995); hei 7-105780 (Apr. 28, 1995); hei 7-244029 (Sep. 22, 1995); hei 8-110712 (May 1, 1996); hei 10-27202 (Feb. 9, 1998); hei 10-84137 (Mar. 30, 1998); and hei 10-208635 (Jul. 8, 1998) disclose heat-pipe equipped fusing roller apparatus.
Such fusing roller apparatus using heat-pipes can be instantaneously heated, thereby reducing power consumption. Fusing roller apparatus also have a short period of delay when switching between stand-by and a printing operation. In particular, the fusing roller apparatus disclosed in Japanese Patent Application Nos. hei 5-135656; hei 10-84137; hei 6-29663; and hei 10-208635 employ different types of heat sources at one end of the fusing rollers, that are positioned beyond the fixing areas. The arrangement of the heat source for each of these fusing roller apparatus increases the volume of the fusing roller apparatus and requires complex structures. Thus, there is a need to improve the structural complexity of such fusing roller apparatus.
The fusing roller apparatus disclosed in Japanese Patent Application Nos. sho 58-163836; hei3-107438; hei3-136478; hei6-316435; hei7-65878; hei7-105780; and hei7-244029 have their heat sources located within their fusing rollers, so that there remains a problem attributable to the increased volume of this apparatus described above. A plurality of local heat pipes, however, are installed for each fusing roller, thereby complicating fabrication and manufacture of the fusing roller apparatus. The local arrangement of the heat pipes moreover, causes temperature deviations between heat-pipe contact portions and heat-pipe non-contact portions.
To solve these and other problems in the art, it is an object of the present invention to provide an electrophotographic image forming apparatus and process.
It is another object to provide an improved fusing roller and fusing process.
It is still another object to provide a fusing roller apparatus for an electrophotographic image forming apparatus, in which local temperature deviation of a fusing roller is sharply reduced, thereby improving overall thermal distribution characteristics.
It is yet another object of the present invention to provide a fusing roller apparatus for an electrophotographic image forming apparatus, which is easy to manufacture and is designed to minimize any increase in the size of the fusing roller apparatus.
It is still another object to provide a fusing roller able to progress from its standby state to its printing state in a shorter period of time.
It is also an object to provide a more energy efficient electrophotolithographic process and apparatus.
To achieve these and other objects of the present invention, in a first embodiment there is provided a fusing process and roller apparatus that may be practiced with a cylindrical fusing roller with both ends sealed; the interior cavity of the fusing roller is evacuated down to a predetermined pressure. The interior cavity of the fusing roller contains a predetermined amount of a working fluid; and a heat-generator is installed in the fusing roller in contact with the working fluid.
A second embodiment of the fusing process and roller apparatus may be practiced with a cylindrical fusing roller that has its axially opposite ends sealed and the interior cavity of the fusing roller is evacuated down to a predetermined pressure. The interior cavity of the fusing roller contains a predetermined amount of a working fluid. A partition divides the inner space of the fusing roller into a plurality of unit spaces. A heat-generator installed in the fusing roller surrounds the partition and is in contact with the working fluid.
For a fusing roller apparatus constructed as either the first or second embodiment of the present invention, it is preferable that the heat-generator is constructed as a spiral-shaped helical coil of a resistance heating element and that both leads of the resistance heating coil extend out from the fusing roller through axially opposite ends of the fusing roller. It is preferable that the heat-generator be arranged helically along and be placed in direct contact with the inner surface of the fusing roller. To enhance the contact force of the heat-generator against the inner wall of the fusing roller, it is preferable that the heat-generator have an outer diameter that is greater than the inner diameter of the interior cavity of the fusing roller so that the heat-generator is elastically compressed in a force fit against the interior cylindrical surface of the fusing roller due to the force created by the differences in diameter. It is preferable that the fusing roller be formed of either copper (Cu) or stainless steel. If the fusing roller is formed of copper, distilled water is preferred as the working fluid. The amount of the liquid phase of the heating medium, that is, the liquid phase of a working fluid contained in the fusing roller, maybe in the range of 5-50% by volume, and preferably with a range of 10-15% by volume, based on the volume of the interior cylindrical cavity of the fusing roller.
For the third embodiment of the fusing roller apparatus, it is preferable that the partition be constructed with a plurality of dividers that are radially arranged.
In a second embodiment of the fusing roller apparatus constructed according to the principles of the present invention, a fusing roller apparatus may be constructed with a cylindrical fusing roller including an outer tube having a first diameter and an inner tube having a second diameter that is smaller than the first diameter coaxially positioned inside the outer tube to form an annular space between the outer tube and the inner tube. The annular space of the fusing roller is evacuated down to a predetermined pressure. A predetermined amount of a working fluid that is smaller than the volume of the annular space formed between the outer tube and the inner tube, is contained within the annular space of the fusing roller. A heat-generator is installed either inside the inner tube or in the annular space.
For the third embodiment of the fusing roller apparatus, it is preferable that the heat-generator be constructed with a first heater installed in the annular space or/and a second heater be installed inside the inner tube. It is preferable that the first heater is a spiral resistance heating coil and that the second heater is a halogen lamp. For the third embodiment of the fusing roller apparatus, it is preferable that the partition be constructed with a plurality of dividers that are radially arranged. It is also preferable that the plurality of partitions divide the annular space into plurality of unit spaces. A fusing roller apparatus constructed as a third embodiment of the present invention may be modified to incorporate one or more of the structural features of the first and second embodiments of the fusing roller apparatus, in accordance with the principles of the present invention.